As a rule of thumb: wij, zij, mij are stressed, and we, ze, me are unstressed. For example: voor MIJ, but VOOR me. Most of the time we use unstressed pronouns, but if we want to emphasize or contrast the pronoun with something else, then the stressed form is used:
We gaan naar huis. vs.
WIJ gaan naar huis maar JULLIE blijven hier.
This is somewhat comparable to the French "je" vs. "moi, je" or the Italian null pronoun vs. "io".
However, in Dutch formal written language you might find the wij, zij, mij forms more often than they would normally be used in informal spoken language.